Organic EL light emitting display device and method of manufacturing the same

ABSTRACT

Disclosed is a method for manufacturing an organic EL light emitting display device, comprising forming an anode electrode above a substrate, forming an organic light emitting layer above the anode electrode, performing a fluorinating treatment on a surface of the organic light emitting layer, and forming a cathode electrode directly on the fluorinated surface of the organic light emitting layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/891,506, filed Jul. 15, 2004 now U.S. Pat. No. 7,247,886 and claimsthe benefit of priority from prior Japanese Patent Application No.2003-326039, filed Sep. 18, 2003, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic EL light emitting displaydevice and a method of manufacturing the same.

2. Description of the Related Art

Recently, an electroluminescence (EL) light emitting display deviceusing a multi-layered film of an organic material attracts attention.The organic EL light emitting display device comprises an organic lightemitting layer sandwiched between an anode electrode formed of ITO and acathode electrode. If a DC voltage is applied between the anodeelectrode and the cathode electrode, electrons are injected from themetal forming the cathode electrode into the low unoccupied molecularorbital (LUMO) of the organic compound constituting the electrontransport layer. On the other hand, holes are injected from the ITOelectrode constituting the anode electrode into the high occupiedmolecular orbital (HOMO) of the hole transport layer. As a result, theholes and the electrons are recombined within the organic light emittinglayer so as to emit light. The method of manufacturing an organic ELlight emitting display device can be roughly classified into twomethods, i.e., into a method of the vapor deposition of molecules havinga low molecular weight under vacuum and a method of coating a polymersolution.

In an organic EL light emitting display device, a metal having a lowwork function is used for forming the cathode electrode that islaminated on the organic light emitting layer because this enhances theefficiency of injecting electrons into the organic light emitting.However, the organic EL light emitting display device using a metalhaving a low work function for forming the cathode electrode isdefective in that the organic EL light emitting display device tends tobe degraded. It is impossible to obtain an organic EL light emittingdisplay device having a sufficiently long life even if an inorganiccompound layer (buffer layer) formed of a fluoride of an alkali metal ora fluoride of an alkaline earth metal is sandwiched between the organiclight emitting layer and the cathode electrode.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amethod for manufacturing an organic EL light emitting display device,comprising forming an anode electrode on a substrate; forming an organiclight emitting layer above the anode electrode; performing afluorinating treatment on a surface of the organic light emitting layer;and forming a cathode electrode directly on the fluorinated surface ofthe organic light emitting layer.

According to another aspect of the present invention, there is provideda method for manufacturing an organic EL light emitting display device,comprising forming an anode electrode above a substrate; forming anorganic light emitting layer above the anode electrode; forming anelectron injection and transport layer formed of an organic materialabove the organic light emitting layer; performing a fluorinatingtreatment on a surface of the electron injection and transport layer;and forming a cathode electrode directly on the fluorinated surface ofthe electron injection and transport layer.

According to another aspect of the present invention, there is providedan organic EL light emitting display device, comprising an anodeelectrode formed above a substrate; an organic light emitting layerhaving a first surface facing to the anode electrode and a secondsurface, and formed above the anode electrode, the organic lightemitting layer comprising a molecules having a carbon-fluorine bond, thenumber of molecules having the carbon-fluorine bond, which are presenton the second surface, being larger than that of the molecules, whichare present inside the organic light emitting layer; and a cathodeelectrode formed directly on the second surface of the organic lightemitting layer.

Further, according to a further aspect of the present invention, thereis provided an organic EL light emitting display device, comprising ananode electrode formed above a substrate; an organic light emittinglayer formed above the anode electrode; an electron injection andtransport layer formed of an organic material, the electron injectionand transport layer having a first surface facing to the organic lightemitting layer and a second surface, and formed above the anodeelectrode, the electron injection and transport layer comprising amolecules having a carbon-fluorine bond, the number of molecules havingthe carbon-fluorine bond, which are present on the second surface, beinglarger than that of the molecules, which are present inside the electroninjection and transport layer; and a cathode electrode formed directlyon the second surface of the electron injection and transport layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross sectional view schematically showing the constructionof a part of an organic EL light emitting display device according toone embodiment of the present invention;

FIG. 2 is a cross sectional view showing the construction of an organicEL light emitting display device for Example 1 of the present invention;and

FIG. 3 is a graph showing the brightness degradation behavior of theorganic EL light emitting display devices for Example 1 of the presentinvention and for Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail.

As a result of extensive research on the conventional organic EL lightemitting display device including a cathode electrode formed of a metalhaving a low work function, the present inventors have found that thedisplay device is degraded by the reaction between the metal having alow work function and the molecule contained in the organic lightemitting layer. Where a buffer layer is formed in a manner to preventthe direct contact between the organic light emitting layer and themetal having a low work function, the display device is degraded by thediffusion of the ions of the inorganic compound constituting the bufferlayer into the organic light emitting layer. Since the moleculescontained in the organic light emitting layer and the diffusion of theions into the organic light emitting layer cause the carrier block andthe carrier trap, the brightness of the light emission is lowered.

Under the circumstances, the present inventors have found that, in orderto obtain an organic EL light emitting display device having a long lifeof light emission, it is necessary to lower the reactivity of themolecules, which are contained in the organic light emitting layer andwhich are brought into contact with the metal having a low workfunction, so as to arrive at the present invention. Where an electroninjection and transport layer made of an organic material is interposedbetween the cathode electrode and the organic light emitting layer, itis possible to lower the reactivity of the molecules contained in theelectron injection and transport layer. It should be noted that themetal having a low work function such as Li, Na, K, Rb, Cs, Mg, Ca, Sror Ba exhibits a high reactivity with the organic light emitting layeror the electron injection and transport layer. Such being the situation,it is necessary to lower sufficiently the reactivity in the case ofusing such a metal having a low work function for forming the cathodeelectrode. It is possible to use a metal having a work function that isnot excessively low, e.g., Al, Ag, Ga, V, Ti, Bi, Sn, Cr, Sb, Cu, Co, orAu, for forming the cathode electrode. Even in this case, it isnecessary to lower the reactivity of the organic light emitting layer orthe electron injection and transport layer in order to prevent similarlythe degradation and the ion diffusion. A similar situation is broughtabout even in the case where a complex between a metal having a low workfunction and another metal having a work function that is notexcessively low is used forming the cathode electrode.

In order to lower the reactivity of the organic light emitting layer andthe electron injection and transport layer, the organic light emittinglayer is subjected to a fluorinating treatment after formation of theorganic light emitting layer or the electron injection and transportlayer and, then, the cathode electrode is formed on the fluorinatedsurface.

If a fluorinating treatment is applied to the organic light emittinglayer on the side of the cathode electrode before formation of thecathode electrode, the carbon-hydrogen (C—H) bond portion of themolecule present at the interface of the organic light emitting layer isconverted into the carbon-fluorine (C—F) bond, with the result that thehydrogen withdrawing reaction is unlikely to be caused by the metalhaving a low work function. In this case, the molecules having thecarbon-fluorine bond are present in a manner to have a gradient that theconcentration of the particular molecules at the interface of theorganic light emitting layer is rendered higher toward the cathodeelectrode. It follows that the energy level is formed stepwise so as toenhance the electron injection efficiency, thereby improving the lightemission efficiency.

The molecule having the carbon-fluorine bond, which securely permitsenhancing the electron injection efficiency, is considered not tocontribute to efficient light emission. Such being the situation, it isdesirable for the organic light emitting layer to have a thickness ofabout 20 to 200 nm. It is also desirable for about 5 to 50% in athickness direction of the organic light emitting layer to be subjectedto the fluorinating treatment. Where the thickness of the organic lightemitting layer exceeds 200 nm, it is necessary to increase the drivingvoltage. Also, the injected electrons or holes tend to be deactivated soas to lower the probability of the electron-hole recombination, with theresult that the light emitting efficiency of the organic light emittinglayer tends to be lowered. On the other hand, where the thickness of theorganic light emitting layer is smaller than 20 nm, it is difficult toform the organic light emitting layer uniformly, with the result thatthe organic EL light emitting display devices tend to be renderednonuniform in the light emitting capability. It is more desirable forthe organic light emitting layer to have a thickness falling within arange of between about 80 nm and 120 nm. Also, it is more desirable forabout 15 to 25% in a thickness direction of the organic light emittinglayer to be subjected to the fluorinating treatment.

In this case, the reactivity of the organic light emitting layer islowered so as to prevent the degradation of the organic light emittinglayer and, thus, to prolong the life of the organic EL light emittingdisplay device. Where a fluorinating treatment is not applied to thesurface region of the organic light emitting layer, the reactivity ofthe organic light emitting layer is high compared with the case wherethe fluorinating treatment is applied to the surface region of theorganic light emitting layer. It follows that the reaction between theorganic light emitting layer and the metal having a low work function iscarried out easily so as to degrade the organic light emitting layerand, thus, to shorten the life of the organic EL light emitting displaydevice.

It is desirable for the fluorinating treatment to be carried out by aplasma processing using a gas containing fluorine. For example, it ispossible to modify the surface region of the organic light emittinglayer by bringing the organic light emitting layer into direct contactwith the gas containing fluorine. The fluorine-containing gas includes,for example, NF₃, SF₆, CF₄ and C₂F₆. It is desirable to use afluorocarbon gas such as a CF₄ gas or a C₂F₆ gas for the fluorinatingtreatment because the processing can be performed with a highfluorinating rate.

The fluorinating treatment can be performed by using a plasma processingapparatus that permits ionizing the fluorine-containing gas. In thiscase, the fluorinating treatment can be performed by exposing theorganic light emitting layer to the atmosphere of thefluorine-containing gas forming a plasma. Alternatively, it is possibleto blow the fluorine-containing gas to the organic light emitting layerunder an ionized state. In the case of forming a cathode electrode onthe organic light emitting layer, it is possible for the organic lightemitting layer to be formed of the compound selected from the groupconsisting of anthracene, pyrene, perylene, tetraphenyl butadiene,9,10-bis(phenyl ethyl) anthracene, 8-quinolinolate lithium,tris(8-quinolinol) aluminum, tris(5,7-dichloro-8-quinolinol) aluminum,tris(5-chloro-8-quinolinol) aluminum, bis(8-quinolinol) zinc,tris(5-fluoro-8-quinolinol) aluminum, tris(8-quinolinol) scandium,bis[8-(para-tosyl) aminoquinoline] zinc complex, bis[8-(para-tosyl)aminoquinoline] cadmium complex, 1,2,3,4-tetraphenyl butadiene,pentaphenyl butadiene, poly(para-phenylene vinylene), poly(2-methoxy,5-(2′-ethyl hexoxy)-1,4-phenylene vinylene), poly(3-alkyl thiophene),poly(9,9-dialkyl fluorene), poly-para-phenylene, polycarbonate, andpolynaphtyl vinylene. The compounds exemplified above permit effectivelylowering the reactivity with the cathode electrode without impairing thelight emission.

In the case of forming a cathode electrode on the electron injection andtransport layer made of an organic material, it is possible to use, forexample, tris(8-quinolinol) aluminum, benzothiazole zinc, or3,4,9,10-perylene tetracarboxyl-bis benzimidazole for forming theelectron injection and transport layer. The materials exemplified abovepermit efficiently performing the electron injection and the electrontransport so as to effectively lower the reactivity. It is possible toset the thickness of the electron injection and transport layer at about1 to 50 nm. The organic light emitting layer and the electron injectionand transport layer can be formed of the materials exemplified above bysuitably selecting the forming method from the group consisting of, forexample, the ink jet system, the dipping system, the spin coating systemand the vacuum vapor deposition system.

The content of the fluorine element (component ratio) introduced by thefluorinating treatment can be measured by, for example, an XPS (X-rayphotoelectron spectroscopy).

If the detecting angle is changed in the XPS, it is possible to changethe depth of the sample at which the electrons that are detected arepresent. For example, if the detecting angle is set at 5°, it ispossible to detect the element composition at the depth of about 9 Åfrom the surface of the sample. Also, the element composition at thedepth of about 70 Å from the surface of the sample can be detected, ifthe detecting angle is set at 45°. The component ratio (%) of eachelement with the total amount of the detected elements set at 100% isdetermined by subjecting the organic light emitting layer after theplasma processing to the XPS analysis. If the component ratio of thefluorine element under the detecting angle of 1 to 10° is higher thanthat of the fluorine element under the detecting angle of 45 to 90°, itis reasonable to state that the carbon-fluorine bond content (componentratio) in the molecules constituting the surface region on the side ofthe cathode electrode is higher than the carbon-fluorine bond content(component ratio) in the molecules constituting the region in thevicinity of the interface of the anode electrode or the inner region ofthe film.

Incidentally, in the case of measuring the carbon-fluorine bond contentby, for example, the XPS during the manufacturing process of the organicEL light emitting display device, the measurement should be carried outbefore formation of the cathode electrode by subjecting the surfaceregion of the organic light emitting layer on the side of the cathodeelectrode to the plasma processing. Alternatively, in the case ofmeasuring the carbon-fluorine bond content after manufacture of theorganic EL light emitting display device, the surface region of theorganic light emitting layer on the side of the cathode electrode shouldbe measured by peeling the cathode electrode from the manufacturedorganic EL light emitting display device. In any case, thecarbon-fluorine bond content can be measured by the measuring methoddescribed above.

The description given above covers the case where a cathode electrode isformed on the organic light emitting layer. The description given abovecan also be applied to the case where an electron injection andtransport layer is formed on the organic light emitting layer, and,then, the cathode electrode is formed on the electron injection andtransport layer. In this case, the description given above should beapplied with the organic light emitting layer replaced by the electroninjection and transport layer.

An embodiment of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 is a cross sectional view schematically showing the constructionof a part of the organic EL light emitting display device according toone embodiment of the present invention. Needless to say, the organic ELlight emitting display device and the manufacturing method of theorganic EL light emitting display device according to the embodiment ofthe present invention are not limited to FIG. 1.

As shown in FIG. 1, a transistor 2 for each pixel is formed in atransistor-forming layer 14 on an insulating transparent substrate 1such as a glass substrate. A partition wall 4 made of an insulatingmaterial is formed as a partitioning element of the pixel. Each pixelpartitioned by the partition walls 4 emits a light ray of any of threecolors of R, G, B. To be more specific, the transistor-forming layer 14having the transistor 2 formed therein is formed on the substrate 1, asdescribed above. Further, three pixels comprising a transparentelectrode (anode electrode) 3 made of, for example, ITO, hole transportlayers 5, 6, 7, polymer organic light emitting layers 8, 9, 10, acounter electrode (cathode electrode) 11, and a silver electrode(cathode electrode) 12 are successively formed on the transistor-forminglayer 14. These three pixels are partitioned from each other by thepartition walls 4.

A material emitting a red light (R) is used as the pigment molecule inthe luminescent center of the polymer organic light emitting layer 8.Likewise, a material emitting a green light (G) is used as the pigmentmolecule in the luminescent center of the polymer organic light emittinglayer 9. Further, a material emitting a blue light (B) is used as thepigment molecule in the luminescent center of the polymer organic lightemitting layer 10. These pixels are connected to the transistors 2 eachformed on the substrate 1. Further, a sealing film 13 is formed toconstitute the uppermost layer with a water absorbing polymer layer 15interposed between the sealing layer 13 and the silver electrode(cathode electrode) 12. The water absorbing polymer layer 15 serves toprevent the organic EL light emitting display device from being degradedby water. It is also possible to use a layer loaded with a dry nitrogenin place of the water absorbing polymer. Where the problem ofdegradation is not generated, it is possible to form the sealing layer13 in direct contact with the silver electrode 12.

Voltage is applied between the transparent electrode and the counterelectrode included in any of the pixels by operating the transistor 2 soas to cause any of the polymer organic light emitting layers 8, 9 and 10to emit a light ray of a desired color. To be more specific, the holessupplied from the anode electrode 3 are migrated through the holetransport layers 5, 6, 7 into the polymer organic light emitting layers8, 9, 10. On the other hand, the electrons supplied from the cathodeelectrodes 11 and 12 are migrated into the polymer organic lightemitting layers 8, 9, 10. As a result, the holes and the electrons arerecombined within the polymer organic light emitting layers so as toemit a light ray, and a desired color is observed from the side of thetransparent substrate 1. The organic EL light emitting display deviceaccording to the embodiment of the present invention can be obtained byarranging the particular pixels in a two dimensional direction.

The substrate on which the anode electrode is formed is not particularlylimited. However, a transparent substrate such as a glass substrate isused in the case where the substrate side is used as the light emittingsurface.

The hole transport layer can be formed by using an ink (ink for a holetransport layer) prepared by dispersing in water aggregates of the donormolecules including polythiophene and a derivative thereof and theacceptor molecules including polystyrene sulfonic acid and a derivativethereof. Particularly, it is desirable to use as the aggregate thecombination of polyethylene dioxy thiophene (PEDOT) used as the donormolecule and polystyrene sulfonic acid (PSS) or polystyrene sulfonate(PSS) used as the acceptor molecule. The particular combination isstable both thermally and chemically and, thus, the substrate can becoated easily with the ink having the particular aggregate of thecombination dispersed therein. In addition, the formed film (holetransport layer) is uniform in thickness and exhibits a high lighttransmittance. It is possible for these donor molecules and acceptormolecules to be dispersed in water and to contain alcohol.

The hole transport layer can be formed of the particular ink byemploying any of, for example, the ink jet system, the dipping system,and the spin coating system. After the coating, the solvent (water) isevaporated by using a hot plate or an oven so as to form a film.

In the case of the organic EL light emitting display device performing amulti color display, the polymer organic light emitting layers made ofdifferent materials are used in the pixels differing from each other inthe displayed colors of red, green and blue. Since the ionizationpotential of the polymer organic light emitting layer differs dependingon the material used, the different kinds of pixels (red, green, blue)differ from each other in the value of the optimum ionization potentialof the hole transport layer. In this case, if the coating of the ink forthe hole transport layer is performed by the ink jet system as describedabove, it is possible to form easily the hole transport layer exhibitingthe optimum ionization potential in each kind of the pixel. It iscertainly possible to obtain a prescribed effect by forming the holetransport layer. However, it is not absolutely necessary to form thehole transport layer.

It is desirable for the hole transport layer to have a thickness of 2 to100 nm, preferably 10 to 50 nm. If the thickness of the hole transportlayer is smaller than 2 nm, it is impossible to obtain a uniform film.On the other hand, if the thickness of the hole transport layer exceeds100 nm, the visible light is absorbed. In addition, the driving voltageis rendered somewhat high.

The organic light emitting layer is formed by the method described aboveby using the material described above. In the embodiment of the presentinvention, a fluorinating treatment is applied to the organic lightemitting layer on the side of the cathode electrode.

The organic light emitting layer having a fluorinating treatment appliedon the side of the cathode electrode can be prepared by subjecting thesurface of the organic light emitting layer to a plasma processingafter, for example, formation of the organic light emitting layer andbefore formation of the cathode electrode.

To be more specific, the substrate having an organic light emittinglayer formed thereon by the coating method is put in a chamber of aplasma processing apparatus, e.g., P-3000 manufactured by InternationalPlasma Corporation, so as to expose the organic light emitting layer tothe ionized fluorine gas for several seconds to several minutes. As aresult, the hydrogen atom on the surface of the organic light emittinglayer is replaced by an atomic group containing fluorine. By the plasmaprocessing, the ratio of the fluorine element is increased on thesurface of the organic light emitting layer so as to obtain afluorinated organic light emitting layer.

The plasma processing apparatus is a processing apparatus that ionizesthe fluorocarbon gas. It is desirable to use, for example, a plasmaetching apparatus such as P-3000 manufactured by International PlasmaCorporation as the plasma processing apparatus. The plasma etchingapparatus of P-3000 noted above permits performing the fluorinatingtreatment in several seconds to several minutes, leading to a highproductivity.

In the case of arranging pixels emitting light rays of a plurality ofdifferent colors, it is possible to apply the fluorinating treatment toonly the organic light emitting layer of the pixel that emits a lightray of the color requiring the fluorinating treatment so as to balancethe light emission with the light emitting characteristics of the pixelhaving the fluorinating treatment not applied thereto. It should also benoted that, where the effect produced by the fluorinating treatmentdiffers depending on the color of the emitted light, it is possible tooptimize the light emitting characteristics produced by the fluorinatingtreatment by applying the fluorinating treatment for each color of theemitted light.

In the organic EL light emitting display device according to theembodiment of the present invention, the interface of the organic lightemitting layer with the cathode electrode is low in its reactivity. Itfollows that it is possible to prevent the reaction in question even inthe case of using a metal having a low work function for forming thecathode electrode so as to make it possible to manufacture an organic ELlight emitting display device having a long life. This embodiment isdirected to the case where a cathode electrode is formed on the organiclight emitting layer. However, it is also possible to form an electroninjection and transport layer made of an organic material on the organiclight emitting layer and to form the cathode electrode on the electroninjection and transport layer. In this case, the fluorinating treatmentdescribed above is applied to the electron injection and transport layerso as to obtain a similar effect.

A metal selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca,Sr and Ba can be used for forming the cathode electrode. It is alsopossible to use a metal selected from the group consisting of Al, Ag,Ga, V, Ti, Bi, Sn, Cr, Sb, Cu, Co and Au for forming the cathodeelectrode. Also, the cathode electrode can be formed by, for example,the vacuum vapor deposition method. Further, the cathode electrode canbe formed by using singly any of the metals described above or by usinga composite of the metals described above. It is also possible for thecathode electrode to be of a multi-layered structure including an AlLilayer or an AlMg layer in combination with an Al layer. In theembodiment of the present invention, the reactivity of the organic lightemitting layer (or the electron injection and transport layer) islowered, with the result that the material of the cathode electrode isnot limited so as to make it possible to use an appropriate material.

An Example of the present invention will now be described.

Example 1

This Example is directed to the manufacture of a square organic EL lightemitting display device sized at 1 mm×5 mm and emitting a light ray of asingle color. FIG. 2 is a cross sectional view showing the constructionof the organic EL light emitting display device. As shown in FIG. 2, theorganic EL light emitting display device comprises a glass substrate 1,an anode electrode 3 formed on the substrate 1, a hole transport layer 7formed on the anode electrode 3, a blue polymer organic light emittinglayer 10 formed on the hole transport layer 7 and a cathode electrode 11formed on the blue organic light emitting layer 10.

In the first step, the anode electrode 3 was formed in a thickness of 50nm by the ordinary method on the glass substrate 1. ITO (Indium TinOxide), which is a transparent conductive material, was used for formingthe anode electrode 3.

Then, the hole transport layer 7 was formed on the anode electrode 3. Anink raw material containing a PEDOT•PSS represented by followingchemical formula (1), i.e., BAYTRON (registered trade name) P VP CH8000,manufactured by Bayer Inc., was used for forming the hole transportlayer 7. To be more specific, the anode electrode 3 was coated by thespin coating method with the ink so as to form the hole transport layer7 in a thickness of about 150 Å.

In the next step, the polymer organic light emitting layer 10 was formedby the spin coating method on the hole transport layer 7 by usingpoly[9,9′-dialkylfluorene], i.e., PDAF, which is a blue light emittingmaterial represented by following chemical formula (2):

Further, the substrate was baked on a hot plate at 140° C. for oneminute so as to evaporate the solvent. The thickness of the polymerorganic light emitting layer 10 was found to be 300 Å.

The substrate after the baking treatment was housed in a plasma chamberso as to apply a fluorinating treatment to the surface of the polymerorganic light emitting layer 10. To be more specific, the substrate washoused in the chamber evacuated to form a vacuum state, and afluorocarbon gas, i.e., a CF₄ gas, was introduced into the chamber.Under this condition, the fluorinating treatment was applied for 45seconds under the applied frequency of 13.56 MHz and the power of 300 W.

Finally, a Mg (magnesium) layer was formed in a thickness of about 100nm on the polymer organic light emitting layer 10 having thefluorinating treatment applied thereto so as to form the cathodeelectrode 11 on the polymer organic light emitting layer 10, therebyobtaining an organic EL light emitting display device for Example 1.

Comparative Example 1

An organic EL light emitting display device for Comparative Example 1was manufactured as in Example 1 in respect of the material and themanufacturing method, except that a fluorinating treatment was notapplied to the polymer organic light emitting layer.

FIG. 3 is a graph showing the change in brightness relative to theinitial brightness, covering the cases where the organic EL lightemitting display devices for Example 1 and for Comparative Example 1were driven with the current density of 180 mA/cm² under an environmentof 10⁻⁷ Torr. As shown in FIG. 3, it took 60 minutes for the brightnessof the organic EL light emitting display device for Example 1, in whichthe fluorinating treatment was applied, to be lowered to half theinitial brightness. On the other hand, the brightness of the organic ELlight emitting display device for Comparative Example 1, in which thefluorinating treatment was not applied, was lowered to half the initialbrightness in only about 30 seconds. Clearly, the characteristics as theorganic EL light emitting display device were insufficient inComparative Example 1. In Example 1, a fluorinating treatment wasapplied to the polymer organic light emitting layer so as to lower thereactivity of the organic light emitting layer 10 and, thus, thereaction between the polymer organic light emitting layer 10 and thecathode electrode 11 was unlikely to take place. Such being thesituation, it was possible to prevent the degradation of the organiclight emitting layer 10. On the other hand, in Comparative Example 1, areaction was carried out between the polymer organic light emittinglayer 10 and the cathode electrode 11 so as to degrade the polymerorganic light emitting layer 10.

The embodiment described above covers the case where the cathodeelectrode was formed on the polymer organic light emitting layer.However, it is also possible to form an electron injection and transportlayer on the polymer organic light emitting layer and to form thecathode electrode on the electron injection and transport layer, withsubstantially the same effect. It is also possible to obtain a similareffect even in the case of using an organic light emitting layer formedof a compound having a low molecular weight.

As described above, the present invention provides an organic EL lightemitting display device that permits preventing the degradation of theorganic light emitting layer so as to prolong the life of the displaydevice and also provides the method of manufacturing the particularorganic EL light emitting display device.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method for manufacturing an organic EL light emitting displaydevice, comprising: forming an anode electrode above a substrate;forming an organic light emitting layer above the anode electrode;performing a fluorinating treatment on a surface of the organic lightemitting layer; and forming a cathode electrode directly on thefluorinated surface of the organic light emitting layer, wherein theperforming the fluorinating treatment includes converting acarbon-hydrogen bond in the organic light emitting layer to acarbon-fluorine bond.
 2. The method according to claim 1, wherein thefluorinating treatment is performed by irradiation with a plasma of afluorine-containing gas.
 3. The method according to claim 2, wherein thefluorine-containing gas is at least one fluorocarbon gas selected fromthe group consisting of a CF₄ gas and a C₂F₆ gas.
 4. The methodaccording to claim 1, wherein the fluorinating treatment is performed byblowing a fluorine-containing gas under the state that the organic lightemitting layer is ionized.
 5. The method according to claim 4, whereinthe fluorine-containing gas is at least one fluorocarbon gas selectedfrom the group consisting of a CF₄ gas and a C₂F₆ gas.
 6. The methodaccording to claim 1, wherein the cathode electrode comprises at leastone element selected from the group consisting of Li, Na, K, Rb, Cs, Mg,Ca, Sr and Ba.
 7. The method according to claim 1, wherein the thicknessof the organic light emitting layer is 20 to 200 nm.
 8. The methodaccording to claim 1, wherein the fluorinating treatment is applied to 5to 50% in the thickness direction of the organic light emitting layer.9. A method for manufacturing an organic EL light emitting displaydevice, comprising: forming an anode electrode above a substrate;forming an organic light emitting layer above the anode electrode;forming an electron injection and transport layer formed of an organicmaterial above the organic light emitting layer; performing afluorinating treatment on a surface of the electron injection andtransport layer; and forming a cathode electrode directly on thefluorinated surface of the electron injection and transport layer,wherein the performing the fluorinating treatment includes converting acarbon-hydrogen bond in the organic light emitting layer to acarbon-fluorine bond.
 10. The method according to claim 9, wherein thefluorinating treatment is performed by irradiation with a plasma of afluorine-containing gas.
 11. The method according to claim 10, whereinthe fluorine-containing gas is at least one fluorocarbon gas selectedfrom the group consisting of a CF₄ gas and a C₂F₆ gas.
 12. The methodaccording to claim 9, wherein the fluorinating treatment is performed byblowing a fluorine-containing gas under the state that the organic lightemitting layer is ionized.
 13. The method according to claim 12, whereinthe fluorine-containing gas is at least one fluorocarbon gas selectedfrom the group consisting of a CF₄ gas and a C₂F₆ gas.
 14. The methodaccording to claim 9, wherein the cathode electrode comprises at leastone element selected from the group consisting of Li, Na, K, Rb, Cs, Mg,Ca, Sr and Ba.
 15. The method according to claim 9, wherein thethickness of the electron injection and transport layer is 1 to 50 nm.